A rapid measurement method for BOD in sewage treatment

Abstract

The present invention relates to the technical field of sewage treatment, and in particular to a method for rapid measurement of BOD in sewage treatment. Under anaerobic conditions, facultative anaerobic microorganisms utilize organic matter and nitrate nitrogen in a water sample to be tested to undergo a denitrification reaction. During the process, atomic oxygen in the nitrate nitrogen is utilized to oxidize the organic matter into carbon dioxide and water, while the nitrate nitrogen is reduced into nitrite nitrogen or nitrogen gas. In this process, the amount of oxygen element reduced in the reaction system before and after the reaction is the BOD of the water sample to be tested. Compared with the traditional BOD5, the method of the present invention takes less time and greatly improves the efficiency of detection. At the same time, compared with the aerobic method for BOD5 measurement, the oxygen consumption of aerobic microorganisms is effectively avoided during the process, thereby improving the accuracy of detection and facilitating popularization and use.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for quickly measuring BOD in sewage treatment. Background Art

[0002] BOD is the biochemical oxygen demand of sewage. There are many organic pollutants in sewage. Some organic matter can be metabolized by microorganisms into carbon dioxide and water, while others cannot. We express the amount of organic matter that can be directly degraded by microorganisms by the amount of oxygen required by microorganisms in degrading organic matter. The more oxygen is used, the more biodegradable organic matter there is in the sewage, and the more serious the pollution is. The unit is mg / L.

[0003] The existing method is to use aerobic microorganisms to naturally proliferate and degrade organic matter in the presence of dissolved oxygen, so that the dissolved oxygen is reduced due to respiration. Due to the slow process, the laboratory culture is usually carried out for five days, which is called the five-day biochemical oxygen demand (BOD5). However, in the process of microbial self-proliferation, both the degradation of organic matter and self-proliferation require oxygen. Since the proliferation rate of aerobic microorganisms is considerable, combining the two as the BOD value of sewage is not accurate. At the same time, the experimental preparation work is cumbersome, the time span is as long as 5 days, the culture preparation is complicated, the experimental conditions are strict, the calculation formula is complicated, and it is not easy to use. In addition, the existing method only focuses on the BOD value under aerobic conditions. However, most of the organic matter in sewage assists microorganisms in denitrification and phosphorus removal under anaerobic conditions, and is also oxidized into carbon dioxide and water. This is not paid attention to in the existing methods.

[0004] Therefore, developing a simpler and faster BOD measurement method is of great significance for the accurate and rapid detection of sewage indicators, and also plays a positive and beneficial role in sewage treatment. Summary of the Invention

[0005] The purpose of the present invention is to provide a rapid measurement method for BOD in sewage treatment to solve the problems that the existing measurement method is time-consuming, affected by the proliferation of aerobic microorganisms themselves, and inaccurate.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for rapid measurement of BOD in sewage treatment, comprising the following steps:

[0007] S1. Take the effluent from the aerobic tank of the sewage treatment plant, let it settle, discard the supernatant and take the activated sludge;

[0008] S2. Add a certain amount of water sample to be tested and excess nitrate nitrogen solution to the activated sludge in S1, add water to the volume and stir to homogenize;

[0009] S3. Avoiding full reaction under aeration conditions. After the reaction is complete, measure the contents of nitrate nitrogen and nitrite nitrogen in the reaction solution;

[0010] S4. Calculate the BOD of the water sample to be tested based on the data in S2-S3.

[0011] Furthermore, in the above-mentioned S1, the static settling time is 20 to 30 minutes, and the mud-water interface is clear.

[0012] Furthermore, in the S2, the COD of the water sample to be tested is measured; after adding water to make the volume, the concentration ratio of COD to nitrate nitrogen in the mixed system is 3 to 5:1.

[0013] Furthermore, in the above-mentioned S2-S3, a magnetic stirrer is used, the magnetic spindle speed is 60-100 rpm, and there is no splash on the liquid surface.

[0014] Furthermore, in said S3, sampling is performed at regular intervals during the reaction, and sampling is stopped when the nitrate nitrogen concentration no longer decreases, at which point the reaction is complete.

[0015] Furthermore, in the above-mentioned S4, the difference between the oxygen content in the nitrate nitrogen before the reaction and the oxygen content in the remaining nitrate nitrogen and the generated nitrite nitrogen after the reaction is the BOD of the water sample to be tested.

[0016] Beneficial effects of the present invention:

[0017] 1. The present invention adopts a high-concentration activated sludge method, which is faster and more efficient. Compared with the traditional BOD5 method, the method of the present invention only takes half a day to complete, effectively improving the efficiency of detection.

[0018] 2. The method of the present invention is more accurate. Compared with the traditional BOD5, the method of the present invention is carried out under anaerobic conditions. Under anaerobic conditions, the self-proliferation of facultative anaerobic microorganisms is only 5% of that of aerobic microorganisms, which effectively improves the accuracy of detection and is convenient for promotion and use. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0020] Example 1

[0021] A water sample to be tested was taken, and its COD (chemical oxygen demand) was measured using the dichromate method (HJ 828-2017). The COD in the water sample to be tested was measured to be 425 mg / L.

[0022] Take the effluent from the end of the aerobic tank of the sewage treatment plant and let it stand for 20 to 30 minutes until a clear mud-water interface appears. After the standing is completed, carefully pour out the supernatant and take the remaining activated sludge.

[0023] In this embodiment, 300 mL of activated sludge was taken, 5 mL of sodium nitrate solution with a nitrogen content of 5 g / L and 200 mL of the water sample to be tested were added thereto, and water was added to make the volume 1000 mL. Under aeration conditions (with air holes), a magnetic stirrer was used to stir and mix at 60-100 rpm. The reaction was started when there was no splash on the liquid surface.

[0024] At the beginning of the reaction, the dissolved oxygen content in the mixed solution was measured by the DO electrode to be 0.43 mg / L; at the same time, sampling was immediately taken after the reaction started to measure the initial nitrate nitrogen concentration in the reaction solution (nitrate nitrogen will remain in the activated sludge, and the residual nitrite nitrogen and COD can be ignored), and then sampling was taken every 0.5 h to measure the nitrate nitrogen and nitrite nitrogen contents in the reaction solution (HG 634-2012) until the reaction was complete; it was measured that the nitrate nitrogen content in the reaction solution was 25.7 mg / L at the beginning of the reaction.

[0025] After the reaction is complete (when the nitrate nitrogen concentration no longer decreases and the nitrite nitrogen concentration no longer increases, which generally takes 2.5 to 4 hours), the measurement shows that the remaining nitrate nitrogen content in the reaction solution is 13.3 mg / L, the nitrite nitrogen content is 0.015 mg / L, and the dissolved oxygen content is 0.12 mg / L.

[0026] Therefore, initially, the oxygen content in the reaction solution is:

[0027] Q1=25.7÷14×16×3+0.43=88.54mg / L

[0028] After the reaction is complete, the content of oxygen in the reaction solution is:

[0029] Q2=13.3÷14×16×3+0.015÷14×16×2+0.12=45.75mg / L

[0030] Therefore, the amount of oxygen consumed during the reaction is 42.79 mg / L. Since the water sample to be tested is diluted 5 times, the BOD of the water sample to be tested in this embodiment is about 214 mg / L.

[0031] During the implementation of the method of the present invention, it is necessary to measure the dissolved oxygen content in the reaction solution before and after the reaction. A DO electrode is used in the process. However, in actual operation, when the dissolved oxygen content is low, the measurement of the DO electrode is not accurate and is prone to large errors. Therefore, during the specific implementation of the method of the present invention, the measurement process of the dissolved oxygen content can also be omitted. After omitting this step, on the one hand, the operation is simpler, and on the other hand, it does not cause a significant impact on the measurement results. For example, after removing the dissolved oxygen measurement step as mentioned above, the final calculated BOD is approximately 212 mg / L, which is almost the same as the measured dissolved oxygen and has no impact on the actual project.

[0032] In addition, it should be noted that in this embodiment, the content of nitrite nitrogen generated is relatively low, but in actual engineering, due to the variety of sewage types, such as industrial wastewater, more nitrite nitrogen will be produced. Therefore, nitrite nitrogen must be considered and cannot be omitted. However, the principle is the same and will not be repeated here.

[0033] In actual measurement, a blank reference may also be set, such as replacing the water sample to be measured with tap water or purified water, to illustrate the accuracy of the measurement of the method of the present invention.

[0034] In practical engineering applications, the method of the present invention can also directly estimate the COD value of the effluent. The changes in COD and BOD of the inlet and outlet water satisfy the following relationship:

[0035] COD 进水 -BOD 进水 =COD 出水 +BOD 出水

[0036] In the above formula, BOD is measured by the method of the present invention. The BOD measured by the method of the present invention is an absolute value (the traditional BOD5 is a relative value), where BOD 出水 Can be ignored, that is:

[0037] COD 进水 -BOD 进水 =COD 出水

[0038] In other words, knowing the influent COD and BOD values ​​can estimate the effluent COD value, which is of great significance for the judgment of microbial treatment of industrial wastewater.

[0039] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A rapid measurement method for BOD in sewage treatment, characterized in that: The following steps are involved: S1. Take the effluent from the aerobic tank of the sewage treatment plant, let it settle, discard the supernatant and take the activated sludge; S2. Add a certain amount of water sample to be tested and excess nitrate nitrogen solution to the activated sludge in S1, add water to the volume and stir to homogenize; S3. Avoiding full reaction under aeration conditions. After the reaction is complete, measure the contents of nitrate nitrogen and nitrite nitrogen in the reaction solution; S4, calculating the BOD of the water sample to be tested based on the data in S2-S3; The difference between the oxygen content in nitrate nitrogen before the reaction and the oxygen content in the remaining nitrate nitrogen and the generated nitrite nitrogen after the reaction is the BOD of the water sample to be tested.

2. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the S1, the static sedimentation time is 20 to 30 minutes, and the mud-water interface is clear.

3. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S2, the COD of the water sample to be tested is measured; after adding water to make up the volume, the concentration ratio of COD to nitrate nitrogen in the mixed system is 3-5:

1.

4. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S2-S3, a magnetic stirrer is used, the magnetic spindle speed is 60-100 rpm, and there is no splash on the liquid surface.

5. The method for rapid measurement of BOD in sewage treatment according to claim 1, characterized in that: In the above-mentioned S3, sampling is performed at regular intervals during the reaction process. When the nitrate nitrogen concentration no longer decreases, sampling is stopped, indicating that the reaction is complete.